Regulation of cytosolic HMG-CoA reductase activity in pea seedlings: contrasting responses to different hormones, and hormone-product interaction, suggest hormonal modulation of activity

Isoprenoid products added to reaction mixtures have no effect on HMG-CoA reductase activity. However, in vivo treatment with stigmasterol, cholesterol, ubiquinone or 4-hydroxybenzoic acid inhibits activity in etiolated tissues. The hormones abscisic acid (ABA) and gibberellic acid (GA) have opposite effects: ABA inhibits, and GA has little effect alone but in combined treatments completely overcomes inhibition by ABA or sterol. The results indicate that hormonal modulation contributes to the regulation of cytosolic HMG-CoA reductase activity.